Feedback control apparatus

ABSTRACT

Apparatus for controlling the operation of a device is disclosed in accordance with the teachings of the present invention wherein the actual operation of the device is detected by detecting means and compared to a predetermined standard of performance. Indications of the variance between the actual operation of the device and the predetermined standard of performance are utilized by control function generating means to generate a device control function which adjusts the operation of the device such that the variance is reduced to zero. The device control function is additionally applied to device simulating means which simulates the response of the device to the device control function and generates a simulating function representative of that response. The control function generating means combines the simulating function with the indicated variance to produce the control function which includes a substantially noise-free component indicative of the rate of change of the operation of the device thereby anticipating the future operation of the device.

United States Patent OConnor et al.

[72] Inventors: Ward OConnor, Deanville, N.J.;

William George Van Vliet, Green- [4 Oct. 24, 1972 Primary Examiner-AlanCohan Attorney-Mam & Jangarathis v l [57 ABSTRACT [73] Asslgnee: 15Lumps Company Bloomfield Apparatus for controlling the operation of adevice is disclosed in accordance with the teachings of the [22] Filed:June 18, 1970 present invention wherein the actual operation of thedevice is detected by detecting means and compared [2]] Appl' 47238 to apredetermined standard of performance. Indica- I tions of the variancebetween the actual operation of [52] U.S. Cl. ..137/487.5, 137/86,251/131, the device and the predetermined standard of per- 318/615,318/609 formance are utilized by control function generating 51] Int.Cl. ..G05b 11/42 means to generate a device control function which [58]Field f Search 37 5 3 4 75; 313 15, justs the operation of the devicesuch that the variance 313/616 10 09; 235/15 340/222 is reduced to zero.The device control function is additionally applied to device simulatingmeans which [56] References Cited simulates the response of the deviceto the device control function and generates a simulating functionUNITED STATES PATENTS representative of that response. The controlfunction generating means combines the simulating function g 'f with theindicated variance to produce the control 36 i g on M87 5 function whichincludes a substantially noise-free 2948295 8/1960 13 componentindicative of the rate of change of the g t l 6 operation of the devicethereby anticipating the future 8111C fth d 2,896,655 7/1959 Hartz..,...137/86 opera o e e 2,638,911 5/ 1953 Griswold ..137/86 X 23Claims, 2 Drawing Figures Model 1 I Output D1fferent|otor I Mom-or I 242 s I Error N I Indicator 1 Adder I 3 err 1 23 22 1 are l6 l2 IIntegrator L I 8 Munigululuble Input Vonoble Regulator system ActualOutput Output Monitor Device Model Control Function Generator Fig. I.

Error indicator 3: 28 Tilllilllii m w r i I n 3 4 m M e m m 2 m m m 2 mm m. r 3 e m 2 m m IIII llilllL PATENTED Hill 24 i972 ATTORNEYS SystemRegulator Variable 27 F Kg. 2.

1 FEEDBACK CONTROL APPARATUS This invention relates to automatic controlsystems and, more particularly, to apparatus employing threesimultaneous modes of operation for automatically controlling a device.

Automatic control systems are well known in the prior art for regulatingthe operation of a device. The device may appropriate severalconventional forms such as a signal amplifier, a phase shift system, anelectric motor, a chemical processing plant and other well known devicesadapted to have the operation thereof adjusted for external and internaldisturbances and device load variations. Generally, conventionalautomatic control systems are designed for precise regulation of thedevice in accordance with a predetermined standard which may be adynamic controlling function. These systems may employ feedforwardcontrol or feedback control, or a combination of feedforward control orfeedback controls.

The principle of operation of a feedforward control system is to detectthe presence of disturbances of a variable that might deleteriouslyinfluence the operation of the device and provide compensating factorstherefor. The compensating factors may cancel or minimize thedisturbances, thereby reducing the effects thereof; or may providecorrective action to counteract those effects. Well known feedforwardcontrol systems that utilize minimizing compensating factors employdisturbance sensitive detecting devices coupled to the source of thevariance; a compensating device responsive to the detected variabledisturbance for producing the compensating factor; and a'combiningdevice for combining the variable and the compensating factor wherebythe disturbance is attenuated such that it has no effect on theoperation of the device to which the compensated variable is applied. Anexemplary electrical feedforward control system might include transducermeans for generating an electrical signal representativeof the variable;differential amplifier means for detecting amplitude disturbances of theelectrical signal; inverter means for producing a compensating signalhaving a value proportional to the detected amplitude disturbance and.out of phase therewith; and algebraic summing amplifier means forcombining the representative electrical signal and the compensatingsignal such that the amplitude disturbance of the representativeelectrical signal is effectively cancelled. The signal produced by thealgebraic summing amplifier means may be applied directly to the deviceor translated into a physical quantity compatible with the operation ofthe device. Other conventional electrical feedforward control systemsprovide compensation for phase and frequency disturbances of arepresentative electrical signal in a manner similar to that of theaforedescribed control system.

Typical feedforward control systems that provide corrective action for adevice to counteract the effects of a disturbance of a variable includedisturbance sensing means coupled to the source of the variable andmeans responsive to the sensed disturbance to predict the consequentialperformance of the device thereto and to compute corrective action forthe device. Hence, an electrical feedforward control system whichperforms this process may include a model of the device, to which isapplied the disturbance containing variable, for predicting the effectsthe variable will have on the actual device. A characteristic modelmight comprise an analog representation of the device constructed ofconventional circuit components; or the model might comprise a digitalcomputer, appropriately programmed. The digital computer mayadvantageously compute the necessary corrective action which should beundertaken by the device to oppose the effects of the disturbancescontained in the variable, and supply the device with a signalindicative of that corrective action.

Feedforward control systems are inherently stable in their operationbecause control of the device is independent of the output of thedevice. However, one disadvantage of feedforward control systems is therequirement that all disturbances that might affect the operation of thedevice, including internal disturbances, external disturbances and loadvariations, must be precisely detected. Another disadvantage is therequirement that the operation of the device, its response to changes inthe variable, the time delay in responding to control signals and othercritical factors must be accurately known and capable of absoluteprediction. Accordingly, it is readily apparent that a complex computersystem having high economic considerations, is necessary for suitableoperation of a commercially acceptable feedforward control system.

The limitations described above with respect to conventional feedforwardcontrol systems have resulted in favorable acceptance of the feedbackcontrol system. Prior art feedback control systems, which may assume avariety of forms such as an electrical feedback control system, apneumatic feedback control system or an hydraulic feedback controlsystem, include three basic elements, viz., means for detecting theactual operation of the device; means for comparing the actual operationof the device with a predetermined standard of performance andindicating the deviation therebetween; and means for adjusting theoperation of the device in accordance with the indicated deviation. Inan electrical feedback control system, the actual operation of thedevice may be represented by the value of a variable to be controlled.If the variable is an electrical signal, i.e., voltage or current, thevalue thereof may be indicated as a phase shift, frequency or amplitude.If, however, the variable is a physical quantity such as pressure, forceor the like, an electrical signal proportional thereto may be generatedby well known electrical transducers. Similarly, the predeterminedstandard of performance, to which the variable to be controlled iscompared, is represented by an electrical signal having a predeterminedphase shift, frequency or amplitude. Hence, the deviation between theelectrical signals may be facilely obtained by conventional differentialamplifier means. The output signal produced by the differentialamplifier means is proportional to the algebraic difference between thevariable to be controlled and the predetermined standard and is utilizedto control a final control element which adjusts a manipulatablevariable whereby the performance of the device is regulated. It has beenfound that the variable to be controlled need not be of the sameclassification as the manipulatable variable. For example, the variableto be controlled might be in 3 terms of pressure or current, whereas themanipulatable variable might take the form of. temperature or voltage.Nevertheless, the manipulatable variable will be so adjusted by thefinal'control element as to cause the actual operation of thedevice toconformto the predetermined standardv ofperformance. Thus, the feedbackcontrol system is characterized by operating in a closed loop such thatan error signal proportional to the difference between'actual operationof the device and desired'operation of the device is generated tocontrol the device in a manner to reduce the error signal to zero. v

Simplified feedback control systems have only a single mode ofoperation, commonly referred to as the proportional mode. Theproportional mode of operationadjusts the performance of the device in amanner proportional to the value of the deviation between the plitudeand phase of the control signal so obtained does not vary with frequencyand no time delay is introduced into the control loop. However, it isseen that a deviation between the actual operation of the device and thedesired operation must always be present to produce the control signalto effectautomatic control of the device when the feedback controlsystem operates in the proportional mode.

- A more efficient mode of operation of a feedback control systemincludes a reset, or integral mode. This mode does not requirecontinually presentdeviation between actual performance and desiredperformance to produce a control signal but, rather, continuouslyamplifies the deviation with the passage of time until the deviation 'isreduced to zero. In an electrical feedback control systemoperating inthe reset mode, the control signal is obtained by integrating'the outputsignal produced by the differential amplifier means. When that outputsignal is reduced to zero, the control signal, by the process ofintegration, remains at its immediately preceding value which is theprecise value required to maintain the final control element in thecondition necessary for the actual operation of the device to conform tothe predetermined standard of performance. The amplitude of theintegrated control signal tends to decrease linearly as the frequency ofthe output signal produced by the differential amplifier meansincreases, thereby attenuating undesirable noise signals. Unfortunately,the, frequency dependent characteristics of reset mode operationintroduce time delays in the feedback control loop thereby causing theactual operation of the device to oscillate about the predeterminedstandard of performance. In other words, the control signal will notreach its proper value at the time the output signal produced by thedifferential amplifier means is zero and the performance of the devicecannot be stabilized at zero deviation.

The instability of the reset mode of operation may be compensated byincluding the well known rate mode of operation. This lattermodecontrols the performance to the slope of a graphical representation ofthe output signal and indicates whether the actual operation of thede'viceis approaching the predetermined standard of performance. As isunderstood, the control signal obtained by the rate mode of operation isnot dependent upon the value of the .output signal but only upon theratevof change thereof. Thefinal control element is thereby adjusted inanticipation of future operation of the device; and the device israpidly brought to conform-to the predetermined standard of performance.It is seen that the rate mode of operation introduces a leading factorinto the time of response of the control loop which advantageouslycounteracts the time delay introduced by the'reset mode of operation.However, the amplitude of the differentiated control signal produced inthe rate mode of operation increases linearly with an increase infrequency, thereby amplifying undesirable noise which causes errors inthe feedback control loop.

A typical prior art electrical feedback control system combining theproportional, reset and rate modes of operation is described in US. Pat.No. 2,946,943 which issued to DD. Nye et al., on July 26, 1960.Analogous fluidic feedback control systems are described at pages 22-76through 2280 of the fourth edition of Perrys Chemical EngineersHandbook, published in 1963 by McGraw-Hill,lnc.

. As aforedescribed, the principal disadvantage of prior art feedbackcontrol systems originates with the rate mode apparatus. Amplificationby this apparatus of spurious noise signals that originate incommercially available transducers have resulted in unreliable andunacceptable control systems. If the rate mode is omitted, however, thedeficiencies above-mentioned with respect to proportional mode and resetmode operation are more pronounced. The technique heretofore employed tonegate the effects of amplification of these noise signals has beentoremove the spurious noise signals by conventional filter means.However, a truly effective filter introduces a large delay in theresponse time of the control loop, thereby frustrating theaforementioned advantages derived from rate mode operation.

Therefore, it is an object of this invention to provide apparatus forautomatically controlling the operation of a device.

It is another object of the present invention to provide a feedbackcontrol system for stabilizing the operation of a device in accordancewith a predetermined standard of performance.

It is still another object of the present invention to providesubstantially noise-free apparatus having a minimal time of response forregulating a processing system.

It is yet another object of the present invention to provide a feedbackcontrol system including apparatus operating in a substantiallynoise-free rate mode with a minimal time of response for regulating adevice.

Various other objects and advantages of the invention will become clearfrom the following detailed description of embodiments thereof, and thenovel features will be particularly pointed out in connection with theappended claims.

In accordance with this invention, apparatus for controlling theoperation of a device is provided wherein detecting means detects theactual operation of said device; simulating means for simulating thephysical characteristics of said device produces simulatedrepresentations of the operation thereof in response to a controlfunction; error indicating means produces indications proportional tothe variance between the actual operation of said device and apredetermined standard of performance; and control function generatingmeans responsive to said simulated representations of the operation ofsaid device and said indications produced by said error indicating meansgenerates said control function such that said control function includesa substantially noise-free component indicative of the rate of change ofthe operation of said device whereby the future operation of said deviceis anticipated and present operation of the device is controlled inaccordance therewith.

The invention will be more clearly understood by reference to thefollowing detailed description of exemplary embodiments thereof inconjunction with the accompanying drawings in which:

, FIG. 1 is a block diagram of a control system in accordance with thepresent invention; and

FIG. 2 is a moredetailed block diagram of the apparatus of the presentinvention.

Referring now to the drawings, wherein like reference numerals are usedthroughout, and in particular to F IG. 1, there is illustrated a controlsystem for controlling the operation of a device in accordance with thepresent invention including the device 11, error indicating means 12,control function generating means 13 and simulating means 14. Device 11may be an electrical device, a mechanical device, an electromechanicaldevice or a fluidic device capable of operating on a variable andadapted to vary its operation in accordance with a control function.Illustrative devices may include an electrical amplifier having anadjustable amplification factor for amplifying a current or voltage; anadjustable phase shifter for shifting the phase of a current or voltage;a frequency generator for generating an electrical signal, the frequencyof which may be regulated by a controlling function. Other devices mayinclude speed controlled motors; pressure or temperature controlledprocessing systems; or

mechanical balancing devices. The foregoing devices are characterized byoperating on a variable and producing an indication of the performanceof that operation. For example, an electrical amplifier performs theoperation of amplifying a voltage (the voltage being a variable) theperformance of which is indicated by the value of the amplified voltage.For convenience, the amplified voltage may be considered the controlledvariable and the gain of the amplifier the manipulatable variable.Similarly, in a processing system where the pressure of a fluid must beregulated for proper control of the process, the performance of thatprocess might be indicated by the pressure of the fluid (the pressurebeing the controlled variable) and the flow of the fluid through thesystem might be the manipulatable variable. It is readily seen that themanipulatable variable and the controlled variable need not necessarilybe of the same physical characteristics. This is especially true inindustrial process control systems.

' The controlled variable, which represents the actual operation of thedevice 11 is applied to error indicating means 12 by coupling means 15.If the controlled variable is an electrical signal, coupling means 15may comprise electrical connecting means, such as conducting leads; if,however, the controlled variable is a fluid pressure, i.e., pneumatic orhydraulic pressure,,

coupling means 15 may comprise conduit means. It should be readilyapparent that the controlled variable may be translated into arepresentative electrical signal by well known transducer means.

Error indicating means 12 is adapted to'indicate the variance betweenthe controlled variable and a predetermined standard of performance,commonly referred to as the set point. The predetermined standard ofperformance may be represented by a physical quantity compatible withthe controlled variable and is supplied to error indicating means 12 viaconnecting means 16. Thus, if the controlled variable is an electricalvoltage, the predetermined standard of performance may be an electricalvoltage. Similarly, if the controlled variable is a fluidic pressure,the predetermined standard of performance may be a fluidic pressure. Thevariance indicated by the error indicating means 12 is applied tocontrol function generating means 13 wherein it is combined with afurther function to generate the control function for regulating theoperation of device 11. Conveniently, the control function may obtain aphysical quantity similar to that of the controlled variable. Thecontrol function is additionally supplied to simulating means 14 whichutilizes the control function to produce the aforementioned furtherfunction. The simulating means 14 may be a model of the device 11 and isadapted to produce the further function in response to the suppliedcontrol function; hence, the further function is a simulatedrepresentation of the controlled variable supplied to connecting means15 by device 11. Simulating means 14 may comprise a simple andeconomical electrical analog of device 1 1, which analog admits of atime constant substantially equal to the time constants of the device,and a transfer function substantially identical to the transfer functionof device 11; or simulating means 14 may comprise a mechanical orfluidic analog of device 11. Typical electrical analogs are manufacturedby Electronics Associates, Incorporated of Long Branch, New Jersey. Ifdesired, simulating means 14 may comprise a programmed digital computer.It, of course, is understood that the structure of simulating means 14is dependent upon the choice of components employed in the controlsystem of the present invenconnecting means 15 with the electricalvoltage representative of the actual operation of device 11, and viaconnecting means 16' with an electricalvoltage representative of thepredetermined standard of performance to which the operation of device11 is to conform. If both voltages applied to error indicating means 12are DC voltages, the variance therebetween may be indicated by a voltage(hereinafter the error signal) which is a DC voltage proportional to thealgebraic difference between the applied voltages. Accordingly,-

err-orindicating means 12 may be conventional differential amplifyingmeans. It is understood by those skilled in the art that the voltagesapplied to error indicating means 12 maybe AC voltages, whereby theerror signal produced by differential amplifying means is'also an ACvoltage. In addition, if the actual operation of the device isrepresented by the phase of an electrical signal, error indicating means12 may comprise phase comparison means for generating an error signalproportional to the difference in phase of the signals provided byconnecting means 15 and 16, respectively.

Control function generating means 13 is supplied with the error signalproduced by error indicating means 12, and combines the error signalwith a simulating signal produced by simulating means 14, whichsimulating signal denotes the simulated operation of device 11, toproduce a device control signal. A detailed explanation of the operationof control function generating means 13 is deferred for the present timeas such explanation is not necessary for an adequate understanding ofthe operation of the apparatus of FIG. 1. The device control signal isapplied to the device 11 in a manner that regulates the operationthereof so that device 11 operates in accordance with thepredetermined'standard of performance. In other words, the 'devicecontrol signal adjusts the operation of device 11 whereby the signalappearing on connecting means 15 tends to obtain a value equal to thatof the signal appearing on connecting means 16, and the error signal isreduced to zero. If device 1 1 is an electrical amplifier, the devicecontrol signal applied thereto might be an automatic gain controlsignal. Similarly, if device 11 is a process control system, the devicecontrol signal might be a valve control signal, for example. Sinceindications of the actual operation of device 11 are employed toregulate the operation thereof, or otherwise stated, an output signal ofdevice 1 1 controls an input signal applied thereto, it is readily seenthat the control apparatus of FIG. 1 functions as a feedback controlsystem.

As illustrated in FIG. 1, the device control signal produced by controlfunction generating means 13 is additionally applied to simulating means14. Whereas simulating means 14 is a model of the device 11, the signalproduced thereby in response to thedevice control signal issubstantially equal to the signal appearing on connecting means 15.Hence, simulating means 14 responds to the device control signal in thesame produced by simulating means 14. The simulated signal, which is anoise-free indication of the actual operation of device 11, is combinedwith the error signal in control function generating means 13 to producethe control signal in a-manne'r subsequently described. It isreadilyseen that simulating means 14 may comprise a digital computer,appropriately programrned to function as a replica of the device 1 1.

FIG. 2 is a more detailed block diagram of the feedback control systemillustrated in FIG. land comprises a processing system 28, inputregulating means 27, operation monitoring means 29, error indicatingmeans 12, control function generating means 13 and simulating means 14.Input regulating means 27 may comprise a conventional final controlelement such as a Fisher valve or a Conoflow valve responsive to apneumatic control signal applied'thereto, or a fluid valve having anelectrically controlled actuator means, well known in the processcontrol art, such as the valves manufactured by Fisher Controls ofMarshalltown, Iowa. Input regulating means 27 is coupled to theprocessing system 28. The processing system 28 is similar to the device11 of FIG. 1 and may comprise a processing plant adapted to operate on aplurality of process variables, and capable of driving a load 30. Forpurposes of simplification, only a single manipulatable process variableis illustrated in FIG. 2. The operation of processing system 28 may bedetected by output monitoring means 29 which may comprise a commerciallyavailable electrical transducer means for generating an electricalsignal in response to the controlled variable applied thereto. It isunderstood that output monitoring means 29 is not limited solely toelectrical transducer means and may typically include means well knownin the prior art to produce a fluidic pressure in response to thecontrolled variable. Connecting means 15 couples output monitoring means29 to error indicating means 12 which, in turn, is coupled to controlfunction generating means 13.

Control function generating means 13 is comprised of rate of changedetecting means 24, gain producing means 23, integrating means 22 andcombining means 25. Rate of change detecting means 24 is adapted toindicate therate of change of a function applied thereto and maycomprise conventional electrical differentiating means whereby an outputsignal proportional to the rate of change of an input signal isproduced. Well known differentiating means may include operationalamplifiers or resistance-capacitance networks or the like. Gainproducing means 23 is designed to produce an output signal proportionalto the value of an applied input signal. The proportionality factor maybe greater or less than unity. Accordingly, gain producing means 23 maycomprise an amplifier or attenuator. If desired, the gain of theamplifier may be adjustable. Integrating means 22 is capable ofcontinuously amplifying an input signal with the passage of time wherebyan output signal proportional to the integral of the input signal isproduced. Integrating means 22 may comprise well known electricalintegrators such as an operational amplifier integrator or aresistance-capacitance circuit commonlyused in the prior art.Combiningmeans 25 may comprise algebraic summation amplifier means toalgebraically add the respective signals produced by rate of changedetecting means 24, gain producing means 23 and integrating means 22. Asindicated in FIG. 2, rate of change detecting means 24 of controlfunction generating means 13 is coupled to simulating means 14, and gainproducing means 23 and integrating means 22 are connected in commontoerror indicating means 12. The output of combining means 25 is coupledto input regulating means 27 and to simulating means 14.

A description of the operation of the control system illustrated in FIG.2 now follows, wherein it is initially assumed that the apparatus shownis electrical apparatus. The operating condition of processing system 28may be detected in the well known manner by monitoring a controlledvariable. Hence, the signal produced by operation monitoring means 29 isa direct representation of the operating condition of processing system28. Connecting means 15 applies this signal to I error indicating means12 wherein it is compared to a predetermined standard of performance asaforedescribed with respect to FIG. 1. Accordingly, the error signalproduced by error indicating means 12 is proportional to the differencebetween an actual output signal of processing system 28 and a desiredoutput signal. Stated otherwise, the error signal is proportional to thevariance between the actual operation of processing system 28 and apredetermined standard to which it is desired the operation ofprocessing system 28 conform. The error signal is received by gainproducing means 23 at an input thereof and an output signal proportionalto the value of the error signal is produced and coupled as a controlsignal component to input regulating means 27 by combining means 25.

Thus, it is seen that input regulating means 27 adjusts the operation ofprocessing system 28 by regulating the manipulatable variable inaccordance with the magnitude of the variance between the actualoperation of processing system 28 and the predetermined standard ofperformance.

The error signal is additionally received by integrating means 22 whichproduces an output signal proportional to the time integral of the errorsignal. This integrated signal is coupled as a control signal componentto input regulating means 27 via combining means 25 whereby theoperation of processing system 28 is controlled accordingly. It shouldnow be apparent that gain producing means 23 provides proportional modecontrol of the processing system 28 and integrating means 22 providesreset mode control thereof.

The aforedescribed disadvantages inherent in proportional mode controland reset mode control are overcome by the present invention in a mannernow explained. Simulating means 14, which was described in detail withrespect to FIG. 1, responds to the control signal applied thereto in amanner which simulates the response of processing system 28. Thus, thesimulated signal produced by simulating means 14 is substantially equalto and varies directly as the signal produced by operation monitoringmeans 29. However, since simulating means 14 is a model of processingsystem 28 and input regulating means 27, represented, for example, by anelectrical analog computer such as that manufactured by ElectronicsAssociates, Incorporated or a digital computer, the simulated signalwill not include undesired spurious noise signals that may be producedby processing system 28 or operation monitoring 10 means 29. The rate ofchange of the simulated signal, which necessarily corresponds to therate of change of the operation of processing system 28, is detected byrate of change detecting means 24 and is coupled as a control signalcomponent to input regulating means 27 via combining means 25.Therefore, it is readily apparent that the rate of change of thesimulated signal provides a prediction of the future operation ofprocessing system 28 and affords an anticipating control therefor.Consequently, the operation of processingsystem 28 is rapidly and stablybrought into conformance with the predetermined standard of performance.Furthermore, the rate of change of the simulated signal will containonly a negligible noise component because the simulated signal producedby simulating means 14 is virtually noise-free.

Although the foregoing has described the operation of an electricalfeedback control system, it should be understood that a fluidic feedbackcontrol system is within the scope of the present invention. Forexample, well known pneumatic or hydraulic pressure devices that areanalogous to the electrical components previously described may beemployed. The differential amplifier that may comprise error detectingmeans 12 may be replaced by fluid pressure proportional control devicesset forth on pages 22-76 through 22-77 and pages 22-79 through 22-80 ofPerrys Chemical Engineers Handbook (4th edition). Integrating means 22may be replaced by the proportional plus reset control mode apparatusdescribed at pages 22-77 and 22-80 of the aforementioned publication.And proportional plus rate control apparatus of the type shown at pages22-77 and 22-80 of the Chemical Engineers Handbook may be substitutedfro the differentiator which may comprise rate of change detecting means24. Alternatively, control function generating means 13 may be replacedby the illustrative proportional-plus-reset-plus derivative stack-typepneumatic controllers described at pages 22-79 through 22-81 of theChemical Engineers Handbook, or by the proportional-plus-resetplus-ratehydraulic controlling means of FIG. 22-l79 on page 22-82 of theaforementioned Handbook. Furthermore, mechanical analogs of theelectrical components illustrated in FIGS. 1 and 2 are well known in theprior art and may be substituted therefor.

While the invention has been particularly shown and described withreference to specific embodiments thereof, it will be obvious to thoseskilled in the art that the foregoing and various other changes andmodifications in form and details may be made without departing from thespirit and scope of the invention. It is, therefore, intended that theappended claims be interpreted as including all such changes andmodifications.

What is claimed is:

1. Apparatus for controlling the operation of a device, said deviceproducing an actual output signal representative of the actual operationthereof, comprismg:

' means for providing a signal indicative of a desired output signal tobe produced by said device;

error detecting means for producing an error signal when said actualoutput signal produced by said device differs from said desired outputsignal;

device simulating means for simulating physical characteristics of saiddevice including the'time constants thereof and responsive to a controlsignal for producing a further signal substantially equal to said actualoutput signal; and control signal generating means coupled to saiderrordetecting means and including differentiating means coupled to saiddevice simulating means for generating said control signal having acomponent proportional to said error signal and another componentproportional to the rate of change of said further signal whereby saidcontrol signal is adapted to be applied to said devices such that saidactual output signal tends to be equal to said desired output signalthereby minimizing said error signal. 2. Apparatus in accordance withclaim lrwherein said control signal generating means further comprises:

amplifying means coupled to said error detecting means for producing asignal proportional to the value of said error signal; and combiningmeans coupled to said differentiating means and said amplifying meansfor combining the signals produced by said differentiating means andsaid amplifying means.

3. Apparatus in accordance with claim 1 wherein said control signalgenerating means further comprises:

integrating means coupled to said error detecting means for producing asignal proportional to the integral of said error signal; and

combining means coupled to said differentiating means and'saidintegrating means for combining the signals produced by saiddifferentiating means and said integrating means.

4. Apparatus in accordance with claim 1 wherein said control signalgenerating means further comprises:

amplifying means coupledto said error detecting means for producing asignal proportional to the value of said error signal;

integrating means coupled tosaid error detecting means for producing asignal proportional to the integral of said error signal; and 1 I.combining means coupled to said differentiating means, said amplifyingmeans and said integrating means for combining the signals produced bysaid differentiating means, said amplifying means and said integratingmeans.

5. Apparatus in accordance with claim 4 wherein said combining meanscomprises algebraic summing means.

6. Apparatus in accordance with claim 4wherein said device simulatingmeans comprises an electrical analog model of said device and saidfurther signal produced thereby is an electrical signal having anegligible noise component.

7. Apparatus in accordance with claim 4 wherein said device simulatingmeans comprises a digital computer model of said device and said furthersignal produced thereby is an electrical signal having a negligiblenoise component.

8. Apparatus in accordance with claim 4 wherein said error detectingmeans comprises differential amplifier means including a first-inputterminal supplied .with said desired output signal and a second inputterminal supplied with said actual output signal whereby said errorsignal is proportional to the algebraic dif ference between said desiredoutput signal and said actual output signal.

9. Apparatus for controlling the operation of a 5 device comprising:

detecting means for detecting the actual operation of said device;simulating means for simulating the physical characteristics of saiddevice, including the time constant thereof; said simulating meansresponding to control functions applied thereto for producing simu-'lated representations of the operation of said tions of the operation ofsaid device whereby the future operation of said device may beanticipated; said component including negligible noise disturbances;

and means for applying said control function to said device so that theactual operation thereof tends to conform in a stable manner to saidpredetermined standard of performance. 10. Apparatus for controlling theperformance of a processing system comprising:

regulating means for regulating a process variable in accordance with acontrol function; monitor means for monitoring the operation of saidprocessing system and for producing indications of 40 the actualoperation thereof;

means for simulating physical characteristics of said regulating meansand said processing system, including the time constants thereof, andresponsive to said control function for producing simulated indicationsof said operation; I error means for generating manifestations of thevariance between the actual operation of said processing system and apredetermined standard of performance;

first means coupled to said error means for producing firstrepresentations of the value of said generated manifestations; secondmeans coupled to said error means for producing second representationsof the integral of said generated manifestations; third means coupled tosaid means for simulating for producing third representations of therate of change of said simulated indications of said operation; and

second and said third representations to produce said control function.11. Apparatus in accordance with claim 10 wherein said means forsimulating comprises a model of said regulating means and saidprocessing system.

12. Apparatus in accordance with claim 11 wherein said model compriseselectrical analog means such that combining means for combining saidfirst, said said simulated indications are electrical signals havingnegligible electrical noise disturbances.

13. Apparatus in accordance with claim 12 wherein said monitor meanscomprises transducer means such that said produced indications areelectrical signals.

14. Apparatus in accordance with claim 13 wherein said error meanscomprises differential amplifier means including a first input terminalsupplied with electrical signals representative of said predeterminedstandard of performance and a second input terminal supplied with saidelectrical signals produced by said transducer means whereby saidgenerated manifestations are electrical signals proportional to thealgebraic difference between said electrical signals representative ofsaid predetermined standard of performance and said electrical signalsproduced by said transducer means.

15. Apparatus in accordance with claim 14 wherein said first meanscomprises electrical amplifying means whereby said first representationsare first electrical signals having amplitudes proportional to the valueof the electrical signals generated by said differential amplifiermeans; said second means comprises electrical integrating means wherebysaid second representations are second electrical signals havingamplitudes proportional to the integral of the electrical signalsgenerated by said differential amplifier means; and said third meanscomprises electrical differentiating means whereby said thirdrepresentations are third electrical signals having amplitudesproportional to the rate of change of said electrical signals producedby said electrical analog means.

16. Apparatus in accordance with claim 15 wherein said combining meanscomprises electrical summation amplifier means such that said controlfunction is an electrical signal proportional to the algebraic additionof said first, said second and said third electrical signals.

17. Apparatus in accordance with claim 16 wherein said regulating meanscomprises control valve means including actuator means responsive tosaid electrical signal produced by said electrical summation amplifiermeans.

18. Apparatus in accordance with claim 11 wherein said monitor meanscomprises pressure transducer means for producing fluid pressures asindications of the actual performance of said processing system.

19. Apparatus in accordance with claim 18 wherein said regulating meanscomprises a final control element.

20. Apparatus in accordance with claim 19 wherein said error meanscomprises pressure responsive means for producing fluid pressuresproportional to the difference between said fluid pressures appliedthereto by said pressure transducer means and a control point to whichsaid pressure responsive means is set, said control point correspondingto said predetermined standard of performance.

21. Apparatus in accordance with claim 20 wherein said first meanscomprises fluid pressure proportional control means whereby said firstrepresentations are fluid pressures linearly proportional to said fluidpressures produced by said pressure responsive means; said second meanscomprises fluid pressure reset control means whereby said secondrepresentations are fluid pressures ropqrtional to the integral of saidpressures produced y said pressure responsive means; and said thirdmeans comprises fluid pressure rate control means whereby said thirdrepresentations are fluid pressures proportional to the rate of changeof said simulated indications of said operation.

22. Apparatus in accordance with claim 21 wherein said combining meanscomprises means in fluid communication with said fluid pressureproportional control means, said fluid pressure reset control means andsaid fluid pressure rate control means such that said control functionis a fluid pressure proportional to said fluid pressures produced bysaid fluid pressure proportional control means plus said fluid pressuresproduced by said fluid pressure reset control means plus said fluidpressures produced by said fluid pressure rate control means.

23. Apparatus in accordance with claim 20 wherein said simulatedindications of said performance produced by said model are characterizedas fluid pressures and wherein said first means, said second means, saidthird means and said combining means are included in aproportional-plus-reset-plus derivative stack-type fluid pressurecontrol means for producing said control function characterized as afluid pressure.

1. Apparatus for controlling the operation of a device, said deviceproducing an actual output signal representative of the actual operationthereof, comprising: means for providing a signal indicative of adesired output signal to be produced by said device; error detectingmeans for producing an error signal when said actual output signalproduced by said device differs from said desired output signal; devicesimulating means for simulating physical characteristics of said deviceincluding the time constants thereof and responsive to a control signalfor producing a further signal substantially equal to said actual outputsignal; and control signal generating means coupled to said errordetecting means and including differentiating means coupled to saiddevice simulating means for generating saId control signal having acomponent proportional to said error signal and another componentproportional to the rate of change of said further signal whereby saidcontrol signal is adapted to be applied to said devices such that saidactual output signal tends to be equal to said desired output signalthereby minimizing said error signal.
 2. Apparatus in accordance withclaim 1 wherein said control signal generating means further comprises:amplifying means coupled to said error detecting means for producing asignal proportional to the value of said error signal; and combiningmeans coupled to said differentiating means and said amplifying meansfor combining the signals produced by said differentiating means andsaid amplifying means.
 3. Apparatus in accordance with claim 1 whereinsaid control signal generating means further comprises: integratingmeans coupled to said error detecting means for producing a signalproportional to the integral of said error signal; and combining meanscoupled to said differentiating means and said integrating means forcombining the signals produced by said differentiating means and saidintegrating means.
 4. Apparatus in accordance with claim 1 wherein saidcontrol signal generating means further comprises: amplifying meanscoupled to said error detecting means for producing a signalproportional to the value of said error signal; integrating meanscoupled to said error detecting means for producing a signalproportional to the integral of said error signal; and combining meanscoupled to said differentiating means, said amplifying means and saidintegrating means for combining the signals produced by saiddifferentiating means, said amplifying means and said integrating means.5. Apparatus in accordance with claim 4 wherein said combining meanscomprises algebraic summing means.
 6. Apparatus in accordance with claim4 wherein said device simulating means comprises an electrical analogmodel of said device and said further signal produced thereby is anelectrical signal having a negligible noise component.
 7. Apparatus inaccordance with claim 4 wherein said device simulating means comprises adigital computer model of said device and said further signal producedthereby is an electrical signal having a negligible noise component. 8.Apparatus in accordance with claim 4 wherein said error detecting meanscomprises differential amplifier means including a first input terminalsupplied with said desired output signal and a second input terminalsupplied with said actual output signal whereby said error signal isproportional to the algebraic difference between said desired outputsignal and said actual output signal.
 9. Apparatus for controlling theoperation of a device comprising: detecting means for detecting theactual operation of said device; simulating means for simulating thephysical characteristics of said device, including the time constantthereof; said simulating means responding to control functions appliedthereto for producing simulated representations of the operation of saiddevice; error indicating means coupled to said detecting means forproducing indications proportional to the variance between the actualoperation of said device and a predetermined standard of performance;control function generating means coupled to said simulating means andsaid error indicating means for generating said control function suchthat said control function includes a component indicative of the rateof change of said simulated representations of the operation of saiddevice whereby the future operation of said device may be anticipated;said component including negligible noise disturbances; and means forapplying said control function to said device so that the actualoperation thereof tends to conform in a stable manner to saidpredetermined standard of performance.
 10. Apparatus for controlling theperformance of a processing system comprising: regulating means forregulating a process variable in accordance with a control function;monitor means for monitoring the operation of said processing system andfor producing indications of the actual operation thereof; means forsimulating physical characteristics of said regulating means and saidprocessing system, including the time constants thereof, and responsiveto said control function for producing simulated indications of saidoperation; error means for generating manifestations of the variancebetween the actual operation of said processing system and apredetermined standard of performance; first means coupled to said errormeans for producing first representations of the value of said generatedmanifestations; second means coupled to said error means for producingsecond representations of the integral of said generated manifestations;third means coupled to said means for simulating for producing thirdrepresentations of the rate of change of said simulated indications ofsaid operation; and combining means for combining said first, saidsecond and said third representations to produce said control function.11. Apparatus in accordance with claim 10 wherein said means forsimulating comprises a model of said regulating means and saidprocessing system.
 12. Apparatus in accordance with claim 11 whereinsaid model comprises electrical analog means such that said simulatedindications are electrical signals having negligible electrical noisedisturbances.
 13. Apparatus in accordance with claim 12 wherein saidmonitor means comprises transducer means such that said producedindications are electrical signals.
 14. Apparatus in accordance withclaim 13 wherein said error means comprises differential amplifier meansincluding a first input terminal supplied with electrical signalsrepresentative of said predetermined standard of performance and asecond input terminal supplied with said electrical signals produced bysaid transducer means whereby said generated manifestations areelectrical signals proportional to the algebraic difference between saidelectrical signals representative of said predetermined standard ofperformance and said electrical signals produced by said transducermeans.
 15. Apparatus in accordance with claim 14 wherein said firstmeans comprises electrical amplifying means whereby said firstrepresentations are first electrical signals having amplitudesproportional to the value of the electrical signals generated by saiddifferential amplifier means; said second means comprises electricalintegrating means whereby said second representations are secondelectrical signals having amplitudes proportional to the integral of theelectrical signals generated by said differential amplifier means; andsaid third means comprises electrical differentiating means whereby saidthird representations are third electrical signals having amplitudesproportional to the rate of change of said electrical signals producedby said electrical analog means.
 16. Apparatus in accordance with claim15 wherein said combining means comprises electrical summation amplifiermeans such that said control function is an electrical signalproportional to the algebraic addition of said first, said second andsaid third electrical signals.
 17. Apparatus in accordance with claim 16wherein said regulating means comprises control valve means includingactuator means responsive to said electrical signal produced by saidelectrical summation amplifier means.
 18. Apparatus in accordance withclaim 11 wherein said monitor means comprises pressure transducer meansfor producing fluid pressures as indications of the actual performanceof said processing system.
 19. Apparatus in accordance with claim 18wherein said regulating means comprises a final control element. 20.Apparatus in accordance with claim 19 wherein said error means comprisespressure responsive means for producing fluid pressures proportional tothe difference bEtween said fluid pressures applied thereto by saidpressure transducer means and a control point to which said pressureresponsive means is set, said control point corresponding to saidpredetermined standard of performance.
 21. Apparatus in accordance withclaim 20 wherein said first means comprises fluid pressure proportionalcontrol means whereby said first representations are fluid pressureslinearly proportional to said fluid pressures produced by said pressureresponsive means; said second means comprises fluid pressure resetcontrol means whereby said second representations are fluid pressuresproportional to the integral of said pressures produced by said pressureresponsive means; and said third means comprises fluid pressure ratecontrol means whereby said third representations are fluid pressuresproportional to the rate of change of said simulated indications of saidoperation.
 22. Apparatus in accordance with claim 21 wherein saidcombining means comprises means in fluid communication with said fluidpressure proportional control means, said fluid pressure reset controlmeans and said fluid pressure rate control means such that said controlfunction is a fluid pressure proportional to said fluid pressuresproduced by said fluid pressure proportional control means plus saidfluid pressures produced by said fluid pressure reset control means plussaid fluid pressures produced by said fluid pressure rate control means.23. Apparatus in accordance with claim 20 wherein said simulatedindications of said performance produced by said model are characterizedas fluid pressures and wherein said first means, said second means, saidthird means and said combining means are included in aproportional-plus-reset-plus derivative stack-type fluid pressurecontrol means for producing said control function characterized as afluid pressure.